1. Field of the Invention
The present invention relates to an angular position adjusting means for adjusting the pivotal angle of a movable member to a desired angular position relative to a fixed member at a relatively high reduction ratio in relative speed with such a function as to damp a shock applied to the movable member.
2. Description of the Prior Art
As an example of the angular position adjusting devices such that the pivotal angle of a movable member can be adjusted manually or by a motor at a high rotative speed reduction ratio and additionally a shock damping function is provided for safety, it is possible to give a mirror adjusting mechanism for an automotive vehicle disclosed in Japanese Utility Model Kokai Publication No. 57-159543 by way of example.
The structure of this mirror adjusting mechanism is as follows: a mirror body is pivotable in the horizontal direction relative to a post attached to a front fender. The mirror body is pivotably supported by a shaft fixed to the post through a spring washer. On a bottom plate of the mirror body, a reduction gear including a motor is fixed. The output gear of the reduction gear is in mesh with a gear fixed to the above-mentioned shaft. When the motor is driven to rotate and move the output gear about the gear fixed to the shaft, the mirror body pivotes about the post against a frictional force of the spring washer. This mechanism is further provided with an electromagnetic device for engaging or disengage a plunger with or from a gear fixed to the shaft in order to determine the stop position of the mirror body.
3. Discussion of the Prior Art
In the above-mentioned structure of the prior art mechanism, however, there exist various problems such that a great space is inevitably required because the reduction gear and the mirror positioning electromagnetic device should be arranged in a mirror rotation plane, and therefore the external decorative design of the fender mirror is restricted or the projection area of the mirror which exerts a harmful influence upon the air dynamics characteristics of the vehicle is inevitably increased.
Further, in this prior art mirror adjusting mechanism, since the relatively heavy reduction gear and the electromagnetic device are arranged at positions remote from the pivotal center of the mirror body, there exists another problem in that vibrations of the mirror body is intensified by vibrations of the running vehicle and therefore it is difficult to obtain a stable rear view through the fender mirror. To overcome the mirror vibration, it is possible to increase the frictional force between a bottom cover of the mirror body and the post by urging the spring washer through the shaft. In this case, however, other problems may arise such that a motor of a higher power or a reduction gear of a higher gear reduction ratio should be incorporated in the mechanism.
Further, this prior art mirror adjusting mechanism is provided with a shock damping function such that the mirror body is rotatable about the shaft in case a shock is applied to the mirror body, for instance, as when a human body hits against the mirror body. In this case, however, since the output gear is inevitably rotated, a shock applied to the mirror is transmitted to the reduction gear. Even if this impact force is small, since the rotative speed is reduced at a high reduction ratio from the motor to the output gear, a very strong impact force is applied to each gear due to the inertia of the motor and the frictional force of each gear bearing portion. Therefore, a large strength against a small impact force is required for the mechanism itself. Further, when the above shock damping function is required from the mirror body to the motor within the mechanism, the reduction gear should be constructed by only spur gears. In other words, it is difficult to utilize a worm mechanism with a high gear reduction ratio in spite of a simple structure for the mirror adjusting device.